CODEWITHSUNDEEP
stringlisthaskell
user3358850
user3358850

Reputation: 129

a Haskell function that converts a list of words to a string

For example:

wordsToString ["all","for","one","and","one","for","all"]
"all for one and one for all"

My code works without a type declaration:

wordsToString [] = ""
wordsToString [word] = word
wordsToString (word:words) = word ++ ' ':(wordsToString words)

But when I do the type check,it shows that it is a list of Chars which seems wrong to me as I'm supposed to declare the input as a list of strings and get a string as the output:

*Main> :type wordsToString
wordsToString :: [[Char]] -> [Char]

I want to change the declaration to wordsToString::[(String)]->[String] but it won't work

Upvotes: 0

Views: 888

Answers (2)

hgiesel
hgiesel

Reputation: 5658

The function is called concat:

concat :: Foldable t => t [a] -> [a]
concat xs = foldr (++) [] xs

In your case, you want to insert a whitespace between the characters. This function is called intercalate:

intercalate :: [a] -> [[a]] -> [a]

It's defined in terms of intersperse.

Upvotes: 1

Daniel Wagner
Daniel Wagner

Reputation: 153212

I want to change the declaration to wordsToString::[(String)]->[String] but it won't work

No, you want to change the declaration to wordsToString :: [String] -> String. You aren't getting a list of strings out, just a single one.

Upvotes: 1

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